Polymerizations of olefins using late transition metal catalysts, that is metals of Groups 6 through 10 (new IUPAC notation) such as Fe, Co, Ni, and Pd have been of interest lately, see for instance World Patent Applications 96/23010, 98/03559, 98/30610, 98/30609, 98/47934, 98/47933, 98/40420 and 98/40374, and U. S. Pat. No. 5,714,556. Catalysts such these are of great interest because besides making known commercial polymers such as high and low density polyethylenes, they are also capable of making polyolefins with new structures.
It is known that hydrogen can be used to lower by chain transfer the molecular weight of polymers produced with many of these catalysts, see World Patent Applications 99/61492 and 99/62963. However, in many instances a relatively large amount of hydrogen is required to get a desired lowering of polyolefin molecular weight.
It is also known that initial (at the start of a polymerization) olefin polymerization rates with these catalysts may be very high resulting in a tendency to overheat the polymerization in its initial stages. This often is undesirable, since it may adversely affect the morphology and/or structure of the polyolefin formed, and/or may reduce the overall productivity of the polymerization catalyst. It may also be desirable to slow the polymerization temporarily when changing polymerization conditions such as pressure and/or temperature, so as to avoid making "transition" material. Therefore a method for controlling olefin polymerization rates with these catalysts without significantly affecting later polymerization and/or the overall catalyst productivity is desired.